S
M
T
W
T
F
S
30
83°
54°
31
85°
55°
1
85°
53°
2
86°
54°
3
86°
52°
4
85°
56°
5
85°
55°
6
84°
56°
7
85°
56°
8
85°
53°
9
83°
54°
10
79°
57°
11
85°
56°
12
81°
54°
13
79°
54°
14
77°
51°
15
78°
51°
16
84°
52°
17
84°
55°
18
84°
54°
19
Hist. Avg.
82°
53°
20
Hist. Avg.
82°
52°
21
Hist. Avg.
82°
52°
22
Hist. Avg.
82°
52°
23
Hist. Avg.
81°
52°
24
Hist. Avg.
81°
52°
25
Hist. Avg.
81°
52°
26
Hist. Avg.
81°
52°
27
Hist. Avg.
81°
52°
28
Hist. Avg.
81°
52°
29
Hist. Avg.
80°
52°
30
Hist. Avg.
80°
52°
1
Hist. Avg.
80°
52°
2
Hist. Avg.
80°
52°
3
Hist. Avg.
80°
52°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Mill Valley
Mill Valley's September 2026 forecast shows daily high temperatures ranging from 77° to 86°, with overnight lows between 51° and 57°. The average high for September is 83° with an average low of 54°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in Mill Valley. See also: October | November | December.
